Various tire components are composed of rubber compositions, particularly rubber compositions which contain particulate reinforcement such as, for example, at least one of rubber reinforcing carbon black and precipitated silica.
Conductive heat transfer can be an important property for many of a tire's rubber components to aid in both transferring heat into the tire as the rubber is being cured at an elevated temperature to thereby promote improved curing of the tire in a shortened period of time and, also, to aid in transferring heat out of a tire which is generated internally within a cured rubber component of the tire as a result of the tire being used to thereby promote improved durability of the tire.
While various additives may be used to promote conductive heat transfer for a rubber composition of a tire component, it a purpose of this invention to evaluate preparation and use of a rubber composition containing a dispersion of graphite platelets for a tire rubber component by first masterbatching a rubber composition with a relatively high concentration of exfoliated graphite platelets by blending the exfoliated graphite platelets in a solvent solution of elastomer (e.g. organic solvent solution of cis 1,4-polyisoprene rubber) or in a dry, or solid, elastomer (e.g. dry, solid cis 1,4-polyisorene rubber).
Carbon may occur in many forms depending somewhat upon its crystallinity and physical configuration. Forms of the carbon may be such as, for example and not intended limiting, diamonds, particulate rubber reinforcing carbon black and graphite. The particulate forms are normally formed, for example, by incomplete combustion of, for example, petroleum or coal products under controlled conditions and particles of the effluent then collected. Rubber reinforcing carbon black is usually in configurations of a composite of carbon particles resembling bunches of grapes. Graphite may sometimes be referred to as being a crystalline allotropic form of carbon which may, for example, be in a shape of powdered, flake, crystal, rod and platelet particles as well as fibers. For this work, use of graphite platelets are to be evaluated. Graphite platelets are understood to be comprised of stacked relatively flat geometric platelet composites (e.g. platelets as stacked individual platelets of composites of hexagonal geometric forms).
The graphite platelets are expected to present little if any, rubber reinforcement quality, as compared to rubber reinforcing carbon black, although it is likely that they generally possess a heat conductive property which may be superior to rubber reinforcing carbon black.
An important aspect of this evaluation is to find, or develop, a way, namely by using a masterbatching method, to provide an adequate dispersion of the graphite platelets within a rubber composition to aid in promoting the aforesaid heat transfer quality for the rubber composition.
In the description of this invention, the term “phr” is used to designate parts by weight of a material per 100 parts by weight of elastomer. The terms “rubber” and “elastomer” may be used interchangeably unless otherwise indicated. The terms “vulcanized” and “cured” may be used interchangeably, as well as “unvulcanized” or “uncured”, unless otherwise indicated.